This invention generally relates to foliage mowing implements which are towed behind and which are mechanically driven by a towing vehicle such as a tractor having a power takeoff (PTO) drive system. More particularly, the invention relates to implements of the type which have a swingable tongue by which the implement is hitched to the towing vehicle. When the towing vehicle is steered through turns, especially when making a turn at the end of a field, the implement undergoes substantial pivoting movement through the swingable tongue or hitch mechanism, thereby necessitating some means for accomplishing pivoting of the mechanical drive mechanism with respect to the implement. The present invention incorporates a gearbox pivotally mounted to the implement, which gearbox has an extension assembly engaged with and responsive to swinging movement of the rear end portion of the mechanical drive assembly.
The present invention finds particular application with respect to so-called center pivot foliage mowing implements such as mower conditioners. An example in this regard is Cicci et al U.S. Pat. No. 4,018,036 which shows a mower conditioner having an arched tongue which is pivotally mounted at the right-to-left center of the mower conditioner. With this general arrangement, the user is able to swing the mower conditioner between the right side and the left side of the pulling vehicle in order to thereby facilitate harvesting operations while reducing crop damage. The general advantages of such a center pivot implement are generally known in the art and are illustrated by this patent, its disclosure being incorporated by reference hereinto.
It is recognized in the art that having the mowing implements hydraulically driven avoids drive train design problems attendant to mechanically transmitting the power needed to drive the crop engagement mechanisms of the implement. Generally speaking, hydraulic conduits more readily accommodate pivoting or swinging movements between components, such as the relatively wide pivoting swings which need to be achieved by a center pivot device of the general type shown in U.S. Pat. No. 4,018,036. However, foliage-engaging mechanisms such as those found in larger mower conditioners and the like, especially including disc mower conditioners, often require more power than can be conveniently provided by hydraulic drive systems. Accordingly, approaches have been put forth for accomplishing mechanical driving of these mechanisms, typically by transferring rotational PTO power through an elongated rotating shaft and to a main gearbox on the implement.
One approach in this regard is to provide arrangements wherein the vertical pivot axis of the swinging tongue is in general vertical alignment with a vertical pivot axis of a pivoting gearbox. In such a "coaxial" arrangement, the mechanical drive shaft and the swinging tongue move in virtual unison with each other in an effort to avoid possible misalignment between the mechanical driving mechanism and the swingable tongue. Patents which exemplify this approach are Ermacora et al U.S. Pat. No. 4,719,742 and Frumholtz et al U.S. Pat. No. 4,899,523, incorporated hereinto by reference. Such a coaxial approach thwarts design freedom and requires an arrangement whereby critical pivoting components must be concentrated in a single area, with one generally on top of the other. These approaches also are complicated by the need in most mower conditioner type implements to allow for up and down pivoting of the implement having the driven mechanisms, such as the header of a disc mower conditioner. While a header or the like usually must be thus pivotable to move between a ground-engaging orientation and a transport orientation, there is no such pivoting relationship between the swingable tongue and the implement. In other words, the respective drive axis and hitch axis often are not truly coaxial during all orientations of the implement.
Mechanical drive arrangements which embody pivoting main gearboxes which are not in alignment with a tongue pivot include those shown in von Allwoerden U.S. Pat. No. 4,858,418 and Pruitt et al U.S. Pat. No. 5,272,859, which are incorporated hereinto by reference. von Allwoerden incorporates a telescoping mechanical drive shaft which is pivotally mounted along a drive axis spaced directly in front of the centrally located hitch axis. The mechanical drive arrangement requires a forked support joint composed of a front part and a rear part joined at a horizontal pivot axis, which is said to accommodate vertical floating movement of the mowing units as they follow the ground contour. This approach relies upon a general movement of the swinging components in order to permit the mechanical driving to proceed at different orientations. There is essentially no direct control mechanism to accomplish these changes.
Pruitt adds a steering structure which directly interconnects the tongue and the rotatable gearbox in order to have the tongue directly turn the pivoting gearbox when the tongue swings from side-to-side. This approach incorporates an added, telescoping structure in order to achieve this steering function, while also utilizing a drive train having opposite joints at equal angles so as to develop a split angle arrangement.